While many people in western North America were enjoying their Christmas dinner, the scientists at the Laser Interferometer Gravitational-Wave Observatories (LIGO) in Hanford, WA and Livingston, LA got a different kind of present -- the second detection of a gravitational wave, the result of two merging black holes an estimated 1.4 billion years ago.
"Unlike our first detection, which was louder than we expected, this second, fainter event was exactly the kind of signal that our computer algorithms were supposed to dig out of the noise," said Michael Landry, Detection Lead Scientist at LIGO Hanford Observatory.
"It is very significant that these black holes were much less massive than those observed in the first detection," says Gabriela Gonzalez, LIGO Scientific Collaboration (LSC) spokesperson and professor of physics and astronomy at Louisiana State University. "Because of their lighter masses compared to the first detection, they spent more time -- about one second -- in the sensitive band of the detectors. It is a promising start to mapping the populations of black holes in our universe."
The first detection of gravitational waves (see earlier SPIE Newsroom article), announced on 11 February 2016, was a milestone in physics and astronomy; it confirmed a major prediction of Albert Einstein's 1915 general theory of relativity, and marked the beginning of the new field of gravitational-wave astronomy.
The second discovery "has truly put the ‘O' for Observatory in LIGO," said Caltech's Albert Lazzarini, deputy director of the LIGO Laboratory. "With detections of two strong events in the four months of our first observing run, we can begin to make predictions about how often we might be hearing gravitational waves in the future. LIGO is bringing us a new way to observe some of the darkest yet most energetic events in our universe."
Fred Raab, Head of LIGO Hanford Observatory, said that after the first detection in September 2015, the initial observing run, planned for three months, was extended another month. "The dedication of our staff in supporting this decision paid off," said Raab. "This signal was detected on the evening of Christmas Day in the Pacific Northwest, but received the scientific designation GW151226, based on the UTC date and time used for astronomy."
The LIGO Observatories are funded by the National Science Foundation (NSF), and were conceived, built, and are operated by Caltech and MIT. The discovery, accepted for publication in the journal Physical Review Letters, was made by the LIGO Scientific Collaboration (which includes the GEO Collaboration and the Australian Consortium for Interferometric Gravitational Astronomy) and the Virgo Collaboration using data from the two LIGO detectors.
SPIE vsited LIGO Hanford in September 2015, before the first detection, and produced the video below.